To date, multipolar fusible links have been used to protect various electrical instruments in an automobile or the like against overcurrent from the battery. As illustrated in FIG. 4(a), a multipolar fusible link 200 known in the art includes: as main components, an input terminal 210; a bus bar 220 having a substantially rectangular shape in a planar view through which an electric current input from the input terminal 210 flows; and a plurality of terminals (240A to 240D) connected to the bus bar 220 via fusible sections (230A to 230D).
The input terminal 210 in the multipolar fusible link 200 is connected to a battery or some other power source, whereas the terminals (240A to 240D) are connected to various electrical instruments. In this way, a configuration in which fuses are provided between the battery or power source and the electric circuits in the electrical instruments is created. If an unexpected high current flows through one of the electric circuits, the corresponding fusible section 230 is heated and blown by the high current, protecting this electrical instrument against overcurrent that would flow through it.
The multipolar fusible link 200 is provided with the fusible sections 230 having different ratings which are connected between the plurality of terminals 240 and the bus bar 220. In the multipolar fusible link 200 illustrated in FIG. 4(a), for example, the fusible section 230A having a rating of 50 A (amperes), which is positioned close to the input terminal 210, is connected to the bus bar 220, and the three fusible sections 230B to 230D each having a rating of 40 A, which are positioned adjacent to the fusible section 230A, are sequentially connected to the bus bar 220. In the drawing, the ratings of the fusible sections are depicted over the terminals 240 to which these fusible sections are connected, for the sake of convenience.
In general, when the rating of a fusible section decreases, its entire length is increased in order to increase its resistance. As illustrated in FIG. 4(b), for example, the fusible section 230E having a rating of 40 A has a shape in which three arms (arms 1, 2, and 3) are interconnected with two links (links 1 and 2). It can be found that the entire length of a fusible section 230E is greater than that of the fusible section 230A having a rating of 50 A illustrated in FIG. 4(a).
As the entire length of a fusible section increases, its height also increases and, as a result, the overall height of the multipolar fusible link with this fusible section increases. In this case, to decrease the height of a fusible section to the maximum extent possible, its shape needs to be changed into a substantially Z shape, as illustrated in FIG. 4(c).
More specifically, as illustrated in FIG. 4(c), an angle β (refer to FIG. 4(b)) between the arms needs to be changed into a smaller angle α1 without changing the entire length of the fusible section (i.e., without changing the lengths of the arms). It can be found that a height Hα1 (see FIG. 4(c)) of a fusible section 230E′ with the angle α1 is less than a height HP (see FIG. 4(b)) of the fusible section 230E with the angle β.
In the multipolar fusible link 200 illustrated in FIG. 4(a), the shapes of the fusible sections 230B to 230D are changed into the shape of the fusible section 230E′ with the height Hα1 illustrated in FIG. 4(c). As a result, the height of the multipolar fusible link 200 is made low, namely, equal to H0=(c0+Hα1+d0). Here, c0 denotes the height of the bus bar 220, and d0 denotes the height of the terminals 240 (the height of all the terminals 240A to 240D is equal to d0).
The angle between the arms has a lower limit that is dependent on design specifications. Herein, it is assumed that the angle between the arms in a fusible section cannot be decreased to less than α1, for convenience of explanation. In addition, it is assumed that when the angle between the arms is set to α1, the height Hα1 of the fusible section can no longer be decreased.
Unfortunately, as described above, if the shape of a fusible section is changed so that the angle between its arms decreases and its height thereby decreases, the lateral width of the fusible section is increased from Lβ (see FIG. 4(b)) of the fusible section 230E to Lα1 (see FIG. 4(c)) of the fusible section 230E′. Consequently, the overall lateral width of the multipolar fusible link including the fusible section 230E′ increases. On the contrary, if the shape of the angle between the arms is greatly changed so that the lateral width of the fusible section decreases and the overall lateral width of the multipolar fusible link thereby decreases, the height of the fusible section 230E increases as illustrated in FIG. 4(b). Consequently, the overall height of the multipolar fusible link increases.
As described above, if the shape of a fusible section is changed so that the overall height of the multipolar fusible link decreases, the overall lateral width of the multipolar fusible link increases. On the other hand, if the shape of a fusible section is changed so that the overall lateral width of the multipolar fusible link decreases, the overall height of the multipolar fusible link increases. This trade-off makes it difficult to determine the height and lateral width of a multipolar fusible link, which can be problematic.